Structural characterization of anhydrite and bassanite obtained by application of solar thermal energy to natural gypsum

MISSCA 2013 (Meeting of the ltalian, Spanish and Swiss Crystallographic Associations). Como, Italia

Natural gypsum is a rock composed principally of CaS04·2H20, along with clays, sand, and salts. It is one of the most widely material s used in the world. Spain is the third largest world producer. For building, gypsum is obtained by calcination of natural rock at different temperatures according to uses. At the end of life, pi aster is considered as Construction & Demolition Waste and vast land is required for its land-filled. Power consumption for gas solid endothermic reactions as dehydration of gypsum is the major cost of this process, and if the energy comes from fossil fuels the environmental cost is high. In this work, solar thermal energy has been applied to the dehydration process of gypsum, in order to study its technological viability. The transformatiori of gypsum into bassanite and anhydrite was followed by X-ray diffraction methods and microscopy techniques (scanning electron and interferometric confocal microscopy). Although the dehydrated process of gypsum is an extended knowledge, the anhydrite phases are highly affected by for different parameters such as: precursors, grain size, the thermal pro ces s used, the heating rate, etc. Samples of gypsum crushed to different grain size, were exposed to solar radiation using a Fresnel len s for period of time ranging between 1-30 mino The crystal parameters of the crystalline phases obtained were determined by application of the Rietveld refinement method to the XRD pattem. Figure 1 shows the textural characteristic of the surface of samples obtained at different states of transformation. Typical texture with fIat and smooth faces in the initial sample contrasts with the increasing of roughness with the exposure time from 0.34 to 0.44 ¡.un. The complete transformation of gypsum into anhydrite was achieved at only 5 rnin of exposure to concentrated solar radiation. The Fresnel lens used allowed to getting temperatures higher than 800 oC at only 1 rnin of exposure.

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